6. Abstract The long-term goal of this proposal is to identify the cis and trans acting systems that target specific RNAs to mitotic microtubules and to understand the function of localized RNAs during mitosis and development. The stable inheritance of genetic material during cell division is critical for the survival and differentiation of all organisims. RNA serves a wide variety of functions within cells, acting both as genetic information in the form of mRNA, and as a structural and catalytic component of various protein complexes. Posttranscriptional regulation of both mRNAs and noncoding RNAs through transport to specific subcellular locations is a widely used mechanism for modulating gene expression in time and space. The localization of different types of RNA to the mitotic spindle is an excellent test case for understanding how localized mRNAs control mitotic spindle function and the inheritance of genetic material. This proposal will use a combination of in vitro and in vivo assays to identify both the cis acting localization sequences that target specific mRNAs to the mitotic spindle during meiosis and throughout development. This information will provide a large increase in the number of known localization elements and provide the information required to build accurate models for the de novo prediction of localized RNAs. Information about mRNA localization elements will be used to biochemically purify and identify trans acting protein factors responsible for the transport of RNA to microtubules, increasing the understanding of the types of systems used to transport specific RNAs to discreet locations within a cell or organism. Finally, the identities of mRNAs localized to the mitotic spindle suggest that localized translation might play a major role in regulation of various mitotic events. This proposal will examine the role of mitotic translation in cell cycle regulation, which will provide insight into translational control of the cell cycle. This proposal will provide the first comprehensive analysis of mRNAs localized to a specific subcellular structure, will provide insight into the systems utilized for mRNA localization, and provide information about the functional role of localized mRNAs in cell cycle control. The experimental approach described here will be generally applicable to understanding the impact of localized RNAs in various cellular processes. 7.